Turbocharged or supercharged engines (i.e. boosted or forced induction internal combustion engines) experience very high operating temperatures. The lubricants used in these engines are exposed to extreme conditions when the engine is stopped, and the lubricant sits in a hot turbocharger as it cools. A lubricant in this environment is prone to the formation of hard deposits in the turbocharger. This phenomenon causes a significant deterioration of turbocharger efficiency and has the potential to cause poor performance and/or severe damage to the engine.
Several published studies have demonstrated that turbocharger use, engine design, engine coatings, piston shape, fuel choice, and/or engine oil additives may contribute to the formation of these deposits in turbocharged engines. Accordingly, there is a need for engine oil additive components and/or combinations that are effective to reduce or prevent the formation of deposits in turbocharged gasoline engines.
Recent specifications such as the 2015 version of the General Motors Dexos1® specification, require passage of a Turbocharger Coking Test. One parameter to determine a passing result in the General Motors Dexos1® Turbocharger Coking Test is maintaining a percent increase to less than a 13% increase in the Turbo Coolant Outside (TCO) Temperature from the 100 cycle TCO Temperature to the 1800 cycle TCO temperature.
There is a need to improve on a simple pass of the 2015 version of the General Motors Dexos1® Turbocharger Coking Test to provide lubricating oil compositions that can score pass ratings of less than a 9.0% increase in the Turbo Coolant Outside (TCO) Temperature from the 100 cycle TCO Temperature to the 1800 cycle TCO temperature. “TCO Temperature Increase” as used herein refers to the percent increase in the TCO Temperature from the 100 cycle TCO Temperature to the 1800 cycle TCO temperature as defined by the formula:
      (                  1800        ⁢                                  ⁢        cycle        ⁢                                  ⁢        TCO        ⁢                                  ⁢        Temperature            -              100        ⁢                                  ⁢        cycle        ⁢                                  ⁢        TCO        ⁢                                  ⁢        temperature              )        100    ⁢                  ⁢    cycle    ⁢                  ⁢    TCO    ⁢                  ⁢          Temperature      .      